*{
    margin: 0;
    padding: 0;
}
#wrap{
    position: relative;
    width: 400px;
    height: 400px;
    margin: 0 auto;
    background: pink;
    .inner{
        position: absolute;
        left: 0;
        right: 0;
        top: 0;
        bottom: 0;
        margin: auto;
        width: 100px;
        height: 100px;
        background: deeppink;
    }
}